Generally, needles are used in sampling of analytical materials such as blood, for diagnosis of various diseases, or drug injection into the body. With the development of various diagnosing techniques and diagnosing chips, the demand for extracting analytical materials from the body has increased. Under such circumstances, a needle which may cause pain during its use and leave an external mark on the skin has hindered the use of such various diagnosing techniques and devices. As a result, microspikes and solid microneedles which are penetration type needles and hollow microneedles which are open tip type needles have been suggested.
Unlike conventional needles, the microneedles should not cause pain when they penetrate the skin, and for such painless skin penetration, the diameter of the upper end part of the needle is a matter to be considered. The microneedle should have a physical hardness sufficient to penetrate the 10-20 μm of stratum corneum. The microneedles should have a length sufficient to reach the capillary vessel for a high efficient analytical material detection and drug delivery. Since in-plane microneedles were suggested (“Silicon-processed Microneedles”, Journal of microelectrochemical systems Vol. 8, No 1, March 1999), various types of microneedles have been developed. For example, a solid silicon microneedle array fabricated using an etching method was suggested as an out-of-plane microneedle array (U.S. Patent Publication No. 2002138049, entitled “Microneedle devices and methods of manufacture and use thereof”). However, since the solid silicon microneedle according to this method was not a hollow structure, it could not be used for analytical material detection in the body and delivery of drugs. As a developed embodiment of an etching technique, a hollow silicon microneedle with an inclination angle was developed by Nanopass Ltd. (W00217985; W02005049107; “Silicon Micromachined Hollow Microneedles for Transdermal Liquid Transport”, Journal of microelectrochemical systems, Vol 12, No. 6, December 2003). Hollow silicon microneedles of side-open type and cross type were suggested by Griss and Steme in Stanford University (“Side-Opened Out-of-Plane Microneedles for Microfluidic Transdermal Liquid Transfer”, Journal of microelectro-chemical systems, Vol. 12, No. 3, June 2003; U.S. patent application No. US2004267205). As such, various hollow silicon microneedles have been developed, but these caused pain upon penetration of the skin owing to their large diameter, and were not efficient in extracting internal analytical materials from the body and drug delivery owing to their length of 500 μm.
A method for preparing hollow metal microneedles was disclosed by Prausnitz, at the University of Georgia, which comprises fabricating a mold by using a laser and then using deposition and electroplating for preparing the microneedles (“Hollow Metal Microneedles for Insulin Delivery to Diabetic Rats”, IEEE Transactions on biomedical engineering, Vol. 52, No. 5, May 2005). However, the hollow metal microneedles prepared by the above method, also had the problem of other conventional methods, with respect to diameter and length. Another method for preparing a novel hollow glass microneedle which has a length of about 900 μm and an inclination angle by extending a glass micropipette, was further suggested by Prausntiz, at the University of Georgia (“Microinfusion Using Hollow Microneedles”, Pharmaceutical Research, Vol. 23, No. 1, January 2006, and “Mechanism of fluid infusion during microneedle insertion and retraction”, Journal of Controlled Release, 2006, 357361). However, this method also failed to prepare hollow microneedles having a diameter (outer diameter) of 50 μm or less. Further, such hollow microneedle made of glass, i.e. a non-conducting substance, had a limitation in its commercialization due to problems in combining it with a variety of electric devices. Although other various types of hollow microneedles have been suggested by 3M, P&G, BD technologies, Alza Corporation and the like, none of these could provide a means to effectively solve the problems connected with diameter, length and hardness. Accordingly, there still has been a great demand for a hollow microneedle which has a diameter fine enough to achieve painless penetration of the skin, a length which is long enough to penetrate the skin to the deeper area, and suitable hardness.